DR. MANTELL ON BELEMNITES, ETC. 
177 
formed by concavo-convex transverse septa or plates. This apparatus has been aptly 
compared by Dr. Buckland to a pile of watch-glasses, gradually diminishing in size 
towards the apex ; the septa are perforated by a tube or siphunculus, which is 
situated on the ventral margin. The phragmocone enlarges upwards, and anteriorly 
to the siphonated part constitutes a large chamber, from the margin of which are 
produced two, or more, long, upright, shelly or calcareous processes, as shown in 
Plate XV. fig. 3, b, b' ; these were probably for the support of the soft parts, or for 
the attachment of muscles. Whether there were similar processes on the opposite 
margin of the chamber cannot be determined, as the peristome is imperfect. 
The figure in outline, Plate XIV. fig. 2, is intended to define these several parts 
more clearly. 
a. a, a. The Capsule, periostricum, or external sheath of the Belemnite, now first de- 
scribed. 
b. The Guard or Osselet, 
c. The apical chambered part of the phragmocone which is situated in the alveolus 
or cavity of the guard. 
d. The visceral or basal chamber of the phragmocone. 
e. e. Two elongated processes produced from the margin of the peristome of the 
visceral chamber ; observed for the first time. 
In the specimens delineated, Plate XV. figs. 1 and 2, the guard is in great part 
covered by the external integument or shelly capsule {d, d, d), which is very thin, 
and resembles in colour and in its glossy appearance, the outer coat or epidermis of 
the phragmocone of the Belemnoteuthis (Plate XIII. figs. 2, 3). The capsule is seen 
adherent to the crushed phragmocone beyond the upper part of the guard in 
Plate XV. fig. 2 ; and in fig. 3 it is shown to be continuous with the horny recep- 
tacle into which it ultimately expands (c"). 
Professor Owen detected on the exterior surface of some spathose guards obtained 
from the Oxford Clay, “ traces of a more immediate investment of a thin friable 
layer of white calcareous matter, analogous to that of the outer layer of the sheath 
of the phragmocone;” but the specimens were evidently too imperfect to demon- 
strate the nature of this periostricum, and its identity with the expanded capsule or 
horny receptacle above ; for the phragmocone is erroneously described as having a 
sheath “continued backwards to line the alveolar cavity, and forwards from its 
basal outlet to form the visceral chamber anterior to the phragmocone*.” 
The appearance of the surface of the phragmocone situated in the alveolus, when 
first exposed by breaking away a portion of the investing guard, is represented, 
Plate XV. fig. 4, a ; and the same specimen with part of the shell removed, to show 
the edges of the plates of the air-chambers, in fig. 5, a. The annular risings and 
depressions on the surface of the shell, fig. 4, a, indicate the situation of the con- 
cavo-convex transverse septa. The phragmocones of the Belemnites in the Oxford 
* Philosophical Transactions, 1844, p. 69. 
I 
